The River Lavant valley is situated at the southern rim of the Alpine main ridge and is enclosed by the mountain ranges of the Saualpe in the west and the Koralm in the east, which are both ranging up to 2100 m. Wolfsberg, the district capital, and St. Andrä are the largest towns in the region. The springs in the two mountain ranges provide most of the drinking and service water for the municipalities.
The River Lavant valley is characterised by low precipitation amounts. With an average annual precipitation of less than 800 mm the valley is one of the driest regions of Carinthia. Moreover, the geological conditions are unfavourable to groundwater storage, the discharges of springs are rather low, and only a limited number of springs can be used for water supply. Due to these natural limitations in water availability, the region has already been affected by water shortages in the past decades, especially during hot and dry summers (EEA 2009; BMLFUW 2016). Significant seasonal bottlenecks in water supply have occurred frequently, e.g., in the years 1993, 2002, 2003 and 2012.
Effects of climate change have been noticeable in the region already during the last decades. Over the last 100 years, there is a clear trend of decreasing annual precipitation in most parts of Carinthia south of the Alpine main ridge. In the Lavant valley region, annual precipitation has decreased by approximately 15–25%, with the strongest seasonal decrease occurring in winter.
Assumedly due to the location of Carinthia at the convergence of Mediterranean and Atlantic climatic influences, model-based regional projections of future trends in precipitation patterns in the south part of Austria have always been subject to high uncertainties and regularly exhibit pronounced variation between climate models. Previous regional scenarios of changes in annual precipitation have ranged from slightly positive to slightly negative trends. Some scenarios projected a significant decline of summer precipitation by up to -15 % from 2050 onwards. The most recent Climate Scenarios for Austria (ÖKS 15) indicate a significant increase in annual mean temperature of +1.3°C (climate mitigation scenario according to RCP4.5) to 1.5°C (business-as-usual scenario according to RCP8.5) for Carinthia and the Lavant Valley up to 2050 (compared to the period 1971-2000). By the end of the century an annual mean temperature increase of up to +4.2 °C may occur in a business-as-usual emission scenario (RCP8.5). The scenarios also show an increase in the annual number of heat days (days with >30 °C). These could increase by +3.2 days by 2050 and rise up to +5.8 or even +17.1 days by the end of the century. As regards annual average precipitation, slight increases are projected in the medium- and long-term, which is mostly due to higher simulated precipitation amounts in the winter season, but all rainfall-related model results are lacking statistical significance. In contrast to temperature projections, future trends in precipitation continue to be characterised by considerably larger uncertainties.
Stronger variability in groundwater levels and deliveries of springs, culminating in recurring periods of water shortage, had been observed already in the years prior to initiation of the adaptation measures. Although the results of regional climate modelling are not straightforward to interpret in terms of their implications for groundwater stocks and groundwater renewal, it is expected that groundwater levels, aquifers and discharges of springs will be affected by increasing variability in the future. This outcome is likely to result from the combined effects of higher inter-annual variability in precipitation regimes, possible decreases in summer rainfall with prolonged periods of drought, higher evapotranspiration rates, and reduced groundwater recharge due to less snowfall and shorter duration of snow cover in winter.
Reduced availability of water resources during dry and hot summer periods coincides with an increase in water demand by households, tourism and agriculture, which in the past has contributed to water supply problems. Since in the central areas of the Lavant valley region further growth in population and settlement areas is expected, this may raise overall water consumption, and thus increase the vulnerability of drinking water supply. Decreasing water availability combined with higher withdrawal rates during dry and hot summer periods were recognized as a threat to continuity of public water supply and created a strong need for response measures by the water management sector.
Forests cover up to 50% of the region’s area, and in particular forest stands at mountain slopes fulfil important water retention functions and protective functions with regard to natural hazards. Due to extensive introduction in altitudes below 900 m in the past, Norway spruce is distributed far beyond its natural range and is by far the dominant tree species in the region. Since spruce trees prefer cool and wet sites, they have in many locations already reached the limits of their tolerance under current climate conditions. Climate-induced multiple stresses on these forests do not only result in productivity losses, but are also threatening their vitality, ecological stability and the delivery of important ecosystem services of forests, such as water retention, water storage, and the protection against gravitational natural hazards.